The Mercator projection is a cylindrical map projection presented by the Belgian geographer and cartographer Gerardus Mercator

Gerardus Mercator

thumb|right|200px|Gerardus MercatorGerardus Mercator was a cartographer, born in Rupelmonde in the Hapsburg County of Flanders, part of the Holy Roman Empire. He is remembered for the Mercator projection world map, which is named after him...

, in 1569. It became the standard map projection for nautical purposes because of its ability to represent lines of constant course

Course (navigation)

In navigation, a vehicle's course is the angle that the intended path of the vehicle makes with a fixed reference object . Typically course is measured in degrees from 0° clockwise to 360° in compass convention . Course is customarily expressed in three digits, using preliminary zeros if needed,...

, known as rhumb line

Rhumb line

In navigation, a rhumb line is a line crossing all meridians of longitude at the same angle, i.e. a path derived from a defined initial bearing...

s or loxodromes, as straight segments. While the linear scale is constant in all directions around any point, thus preserving the angles and the shapes of small objects (which makes the projection conformal), the Mercator projection distorts the size and shape of large objects, as the scale increases from the Equator to the poles, where it becomes infinite.
Mercator's 1569 edition was a large planisphere

Planisphere

A planisphere is a star chart analog computing instrument in the form of two adjustable disks that rotate on a common pivot. It can be adjusted to display the visible stars for any time and date. It is an instrument to assist in learning how to recognize stars and constellations...

 measuring 202 by 124 cm, printed in eighteen separate sheets.